In general, a compressor for an automobile inhales refrigerant discharged after the refrigerant evaporated in an evaporator, converts it into liquescent refrigerant gas of high-temperature and high-pressure, and then, discharges it to a condenser.
There are compressors of various kinds, for example, a swash plate type compressor that pistons perform a reciprocating motion by rotation of an inclined swash plate, a scroll type compressor performing compression by rotation of two scrolls, a vane rotary type compressor performing compression by a rotary vane, and so on.
Out of the above compressors, the reciprocating type compressor compressing refrigerant according to the reciprocating motion of the piston is classified into the swash plate type, a crank type, and a wobble plate type, and the swash plate type compressor is also classified into a fixed capacity type and a variable capacity type according to a use purpose.
FIGS. 1 and 2 are views showing a prior art fixed capacity swash plate type compressor. Referring to the drawings, the fixed capacity swash plate type compressor will be described in brief as follows.
As shown in the drawings, the swash plate type compressor 1 includes a front housing 10 having a front cylinder block 20 therein, and a rear housing 10a coupled with the front housing 10 and having a rear cylinder block 20a therein.
Each of the front and rear housings 10 and 10a has a discharge chamber 12 and a suction chamber 11 formed inside and outside a partition 13 in correspondence with a refrigerant discharge hole and a refrigerant suction hole of a valve plate 61, which will be described later.
Here, the discharge chamber 12 includes: a first discharge chamber 12a formed inside the partition 13; and a second discharge chamber 12b formed outside the partition 13, divided from the suction chamber 11, and fluidically communicated with the first discharge chamber 12a through a discharge hole 12c. 
That is, refrigerant of the first discharge chamber 12a is contracted when it passes through the discharge hole 12c of a small diameter but expanded when it flows to the second discharge chamber 12b. In this instance, pulsating pressure drops to reduce vibration and noise during the contraction and expansion of the refrigerant.
Meanwhile, a plurality of bolt coupling holes 16 are formed on the suction chamber 11 in a circumferential direction. The front and rear housings 10 and 10a are coupled and fixed with each other through the bolt coupling holes 16 via bolts 80 in a state where a plurality of components are assembled inside the front and rear housings 10 and 10a. 
After that, the front and rear cylinder blocks 20 and 20a respectively have a plurality of cylinder bores 21 therein, and pistons 50 are combined to the corresponding cylinder bores 21 of the front and rear cylinder blocks 20 and 20a in such a way that the pistons 50 perform a straight reciprocating motion. In this instance, the pistons 50 are connected to a driving shaft 30 by interposing a shoe 45 on the outer periphery of a swash plate 40 inclinedly mounted to the driving shaft 30.
So, the pistons 50 reciprocate inside the cylinder bores 21 of the front and rear cylinder blocks 20 and 20a while cooperating with the swash plate 40 rotating with the driving shaft 30.
Moreover, valve units 60 are respectively mounted between the front and rear housings 10 and 10a and the front and rear cylinder blocks 20 and 20a. 
Here, the valve unit 60 includes a valve plate 61 having a refrigerant suction hole and a refrigerant discharge hole, and a suction reed valve 63 and a discharge reed valve 63, which are mounted on both sides of the valve plate 61.
The valve units 60 are respectively assembled between the front and rear housings 10 and 10a and the front and rear cylinder blocks 20 and 20a, and in this instance, the position of the valve unit 60 is fixed while fixing pins 65 formed at both sides of the valve plate 61 are inserted into fixing holes 15 formed on the surfaces of the front housing 10 and the front cylinder block 20 and on the surfaces of the rear housing 10a and the rear cylinder block 20a. 
Meanwhile, the front and rear cylinder blocks 20 and 20a have a plurality of suction passageways 22 therein, so that the refrigerant supplied to a swash plate chamber 24 disposed between the front and rear cylinder blocks 20 and 20a is flown to each suction chamber 11, and second discharge chambers 12b of the front and rear housings 10 and 10a are fluidically communicated with each other by connection passageways 23 formed through the front and rear cylinder blocks 20 and 20a. 
Therefore, suction and compression of the refrigerant can be performed simultaneously inside the bores 21 of the front and rear cylinder blocks 20 and 20a according to the reciprocating motion of the pistons 50.
Each of the front and rear cylinder blocks 20 and 20a has a shaft support hole 25 formed at the center thereof to support the driving shaft 30, and a needle roller bearing 26 interposed inside the shaft support hole 25 to rotatably support the driving shaft 30.
Meanwhile, The rear housing 10a includes a muffler 70 formed on the upper portion of the outer periphery thereof to supply the refrigerant transmitted from an evaporator to the inside of the compressor 1 during a suction stroke of the piston 50, and to discharge the refrigerant compressed in the compressor 1 toward a condenser during a compression stroke of the piston 50.
Hereinafter, a refrigerant circulating process of the compressor 1 having the above structure will be described.
The refrigerant supplied from the evaporator is supplied to the swash plate chamber 24 between the front and rear cylinder blocks 20 and 20a through a refrigerant suction hole 71 after the refrigerant is inhaled to a suction part of the muffler 70, and then, flown to the suction chambers 11 of the front and rear housings 10 and 10a along the suction passageways 22 formed in the front and rear cylinder blocks 20 and 20a. 
After that, the suction reed valve 63 is opened during the suction stroke of the piston 50, and in this instance, the refrigerant contained inside the suction chamber 11 is inhaled into the cylinder bore 21 through the refrigerant suction hole of the valve plate.
After that, the refrigerant of the cylinder bore 21 is compressed during the compression stroke of the piston 50, and in this instance, the discharge reed valve 62 is opened, and the refrigerant is flown to the front discharge chambers 12a of the front and rear housings 10 and 10a through the refrigerant discharge hole of the valve plate.
Continuously, the refrigerant flown to the first discharge chambers 12a is discharged to a discharge part of the muffler 70 through a refrigerant discharge hole 72 of the muffler 70 after passing the second discharge chambers 12b, and then, flows to the condenser.
Meanwhile, the refrigerant compressed in the cylinder bore 21 of the front cylinder block 20 is discharged to the first discharge chamber 12a of the front housing 10, flows to the second discharge chamber 12b of the rear housing 10a along the connection passageways 23 formed in the front and rear cylinder blocks 20 and 20a after flowing to the second discharge chamber 12b of the front cylinder block 20, and then, discharged to the discharge part of the muffler 70 through the refrigerant discharge hole 72 together with refrigerant of the second discharge chamber 12b of the rear housing 10a. 
However, the prior art compressor 1 has a disadvantage in that suction volumetric efficiency of refrigerant is decreased due to a loss caused by suction resistance generated by complicated refrigerant flow channels and a loss caused by elastic resistance of the suction reed valve 63 generated during opening and closing of the valve unit 60.
Meanwhile, Korean Patent Laid-open publication No. 2003-47729 discloses a lubricating structure in a fixed capacity piston type compressor, which is a technology to reduce a loss caused by elastic resistance of the suction reed valve 63. That is, the above technology adopts a suction rotary valve integrated with a driving shaft without the suction reed valve, so that refrigerant directly flows from the rear portion of the driving shaft into a cylinder bore through the driving shaft to reduce the loss caused by suction resistance.
However, the prior art has a disadvantage in that the compressor cannot show the optimal compression performance, since refrigerant is inhaled from the rear portion of the driving shaft, and so, a great deal of refrigerant flows into the rear cylinder bore and refrigerant of a small quantity flows into the front cylinder bore.
In addition, the prior art has another disadvantage in that there is a restriction in design, for example, a refrigerant suction part must be formed on the rear portion of the driving shaft.
Moreover, the prior art has another disadvantage in that it is difficult to supply refrigerant of a sufficient amount to the cylinder bores since there is a restriction in enlarging a size of the flow channel formed inside the driving shaft.